Ad6-Based GM-CSF Expressing Vector Displays Oncolytic and Immunostimulatory Effects in an Immunocompetent Syrian Hamster Model of Cholangiocarcinoma

Cholangiocarcinoma (CCA), the second most common liver cancer, remains highly resistant to chemotherapy and radiotherapy, leaving patients with unresectable tumors in urgent need of innovative therapeutic approaches. Adenovirus type 6 (Ad6), a species C human adenovirus, offers significant potential for cancer therapy due to its low seroprevalence compared to Adenovirus type 5 (Ad5) and its ability to evade Kupffer cells during systemic delivery. In this study, we developed a novel oncolytic adenovirus vector based on the Ad6 engineered to express human GM-CSF (Ad6-d24-GM) and evaluated its therapeutic efficacy in a novel immunocompetent, replication-permissive Syrian hamster model of CCA. Intratumoral administration of Ad6-d24-GM significantly suppressed tumor growth and prolonged survival without evidence of toxicity, as indicated by stable body weights and normal liver enzyme levels. Both Ad6-d24-GM and wild-type Ad6 induced robust infiltration of CD4+ and CD8+ T cells, as well as CD68+ macrophages within tumors, demonstrating activation of antitumor immunity. Notably, the Ad6-d24-GM group exhibited a statistically significant increase in CD68+ cells compared to wild-type Ad6, highlighting the immunomodulatory effect of GM-CSF transgene. These results demonstrate the oncolytic and immunostimulatory potential of Ad6-based vectors for CCA treatment and validate the Syrian hamster syngeneic CCA-OF model as a valuable platform for studying oncolytic adenovirus therapies.